This application claims the priority of German patent document 102 42 234.6, filed Sep. 12, 2002 (PCT International Application No. PCT/EP2003/009414, filed Aug. 26, 2003), the disclosure of which is expressly incorporated by reference herein.
This invention relates to a method for determining an exhaust gas recirculation quantity for an internal combustion engine, such as is used as a drive motor for motor a vehicle, for example.
Exhaust gas recirculation is known to offer advantages with regard to fuel consumption and exhaust emissions. The term “quantity” is used for the sake of simplicity, to denote a physical variable indicative of quantity (e.g., the mass or the quantity rate or mass flow rate) of recirculated exhaust gas and/or gas mixture fed into the internal combustion engine.
The quantity of fresh gas fed into the combustion chamber(s) of an internal combustion engine may be measured, for example, via a hot-film mass flow meter (HFM) in a respective intake manifold and/or intake path. The exhaust gas recirculation quantity cannot be determined in this way, however, and is therefore conventionally determined (and known) indirectly for at most a very specific design state, e.g., a normal state of an internal combustion engine without any additional measures. For other engine operating states, and in particular for changing temperatures and changing atmospheric pressure of the environment from which the fresh gas and/or fresh air for the motor is obtained, it is useful to establish a modified exhaust gas recirculation rate in comparison with the design state (i.e., the normal state), in order to be able to comply accurately with emission limits, for example. Therefore there is a need to know exactly the exhaust gas recirculation rate at all points in time in order to be able to regulate it at a suitable level.
German Patent Document DE 199 34 508 A1 describes a method for controlling exhaust gas recirculation, wherein a setpoint exhaust gas recirculation rate is determined on the basis of the engine load, engine torque and air pressure; an actual exhaust gas recirculation rate and the opening and closing movements of a throttle valve are detected by sensors, and an exhaust gas recirculation control valve is operated as a function of the difference between the actual and setpoint exhaust gas recirculation rates as well as a throttle valve opening signal, a throttle valve closing signal and the respective air pressure. The exhaust gas recirculation quantity is determined by sensors based on a measurement of the pressure difference at a throttle opening provided in a respective exhaust gas recirculation line.
U.S. Pat. No. 6,067,800 discloses the determination of the exhaust gas recirculation quantity using an estimate of the fresh gas temperature as a function of influencing parameters.
A method for determining the exhaust gas recirculation quantity is known from generic European Patent 1 221 544 A2, in which the exhaust gas recirculation quantity is determined from an exhaust gas temperature, a fresh gas temperature, a fresh gas quantity, and/or a volumetric efficiency, and the fresh gas temperature is determined by means of a fresh gas temperature model that is adaptively adapted to influencing parameters relevant to the fresh gas temperature.
One object of the present invention is to provide a method of the type defined in the preamble, which permits precise and reliable determination of the exhaust gas recirculation quantity with little effort, in particular at various operating states.
This and other objects and advantages are achieved by the method according to the invention, in which the exhaust gas recirculation quantity is determined from an exhaust gas temperature, a fresh gas temperature, a fresh gas quantity and/or a volumetric efficiency. The fresh gas temperature is determined by a fresh gas temperature model which is adaptively adjusted while the engine is running, adapting it to relevant influencing parameters pertaining to the fresh gas temperature. Volumetric efficiency is a measure of the fresh gaseous supply to the engine. It is defined as the ratio of the total quantity of gas supplied to the engine per operating cycle to the theoretical load, that is, the ratio of the filling per operating cycle to the theoretical fresh load in filling the geometric cubic capacity of the engine with air and/or mixture in the ambient state, when the engine is not supercharged and/or in the state downstream from a compressor and/or a charge air cooler that is provided in an internal combustion engine with supercharging. For operation with exhaust gas recirculation, volumetric efficiency is defined as the ratio of the total quantity of gas mixture supplied per operating cycle to the quantity of gas mixture in filling the geometric cubic capacity of the internal combustion engine with gas mixture in the state after admixture through the exhaust gas recirculation. Volumetric efficiency is also referred to as absorption capacity.
The exhaust gas temperature, a temperature of the recirculated exhaust gas (also known as the exhaust gas recirculation temperature), and the volumetric efficiency are preferably also determined by corresponding models, which are adaptable to relevant influencing parameters pertaining to the respective quantities. Preferably, each of the models comprises a basic model, a correction model and/or a filter block. With the basic model, a basic value is determined for the output variable and/or for a part of the output variable of the corresponding overall model. This basic value is corrected, if necessary, by an output variable of the correction model if certain input variables that are relevant for the output variable of the overall model deviate from predefined reference values and/or reference states. When speaking of a correction model, this in fact refers to a group of correction models having one correction model per input variable. For the determination of deviations, the input variables are monitored, preferably by measurement and subsequent comparison with the reference values. The basic models and/or correction models are preferably engine characteristic maps and/or characteristic lines, but they may also be linear and/or nonlinear mathematical and/or physical simulation models based on differential equations. The basic models and/or correction models may also be neural networks.
Each of the overall models preferably also has a filter block. The filter blocks are preferably first-order delay elements, so-called PT1 elements. However, other filters, preferably dynamic filters, may also be used, such as delay elements of a higher order or delay elements in combination with monostable elements. By means of filtering, a dynamic response is imposed upon an input variable of a filter block, so that a (calculated) output variable of the filter block approximates the real response of the measured equivalent of the output variable. Such filtered variables, i.e., variables determined by filtering, can be adjusted and/or regulated more easily by a regulating and/or controlling means. This is the case with the exhaust gas recirculation rate in particular. It is regulated more rapidly and has less overshooting, which leads to a lower component burden and to more steady emissions, thus preventing emission peaks. Filtering of variables is also known as dynamic correction.
The method according to the invention can be integrated to advantage into a control unit, such as an engine control unit and/or a vehicle control unit which is conventionally present in a motor vehicle, for example. With the method according to the invention, the prevailing exhaust gas recirculation quantity (i.e., exhaust gas recirculation rate) can be calculated with a high precision under steady-state and non-steady-state conditions and under different operating conditions and ambient conditions.
The basic models and correction models are preferably determined in experiments or on a test stand, for example, before market introduction of the internal combustion engine, and are stored in a memory of a control unit of the conventional type. The basic models and correction models are preferably only type-specific, and are not determined in advance for each individual internal combustion engine in this way and then adapted to the individual engine during operation thereof.
The method according to the invention for determining the exhaust gas recirculation quantity does not require any sensors for measuring the exhaust gas recirculation quantity. Even without exhaust gas recirculation quantity sensors, the quantity of recirculated exhaust gas can be determined accurately and reliably. To do so, the models used are adapted by using certain correction models, so the method is automatically adapted to changes occurring during the service life of the engine; such changes would include operating states that deviate from a basic state (e.g., non-steady-state processes, changes in ambient conditions).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.